I want to jailbreak my iphone 3gs which is on iphone firmware 4.3?

i wanna jailbreak my iphone 3gs which is on iphone firmware 4.3 i hav tried downgrading but i failed is there anyway to jailbreak without downgrading n is free if so tel me hw..n if it nids downgrading pls tel me hw too i really hav no idea but this i hav nvr done this b4 n i hav no cydia or anything on my pone yet pls tel me hw to jailbreak or downgrade..?..